The objective of this proposal is to evaluate potent new drugs for smallpox and vaccination complications. Smallpox, caused by the variola virus, is an important bioterrorist threat and although sufficient smallpox vaccine is available, there are a number of reasons to have an FDA approved, orally active antiviral drug which can be self administered. Up to 40 million persons are not good candidates for vaccination including those with AIDS, immunosuppression, organ transplants, cancer chemotherapy and common skin diseases. Exposed persons who are vaccinated too late after exposure may not gain immune protection in time to prevent infection and death. In addition, IL-4 variants of poxviruses have been described which can bypass immune protection of vaccines. For these reasons, an orally active drug for the prevention and treatment of smallpox would be highly desirable. In 1999, our laboratory discovered an orally active lipid ester of cidofovir which shows excellent activity in four animal models of poxvirus disease, both preventing disease and treating disease after infection and this analog is currently in development. Issues have arisen in development which must be overcome if FDA approval is to be obtained. These include toxicity to the GI tract and fast degradation in pivotal monkey models of poxvirus disease which are required for FDA approval under the Animal Equivalence Rule. Recently, we developed a innovative medicinal chemistry paradigm to stabilize poxvirus antivirals like hexadecyloxypropyl-cidofovir (CMX001) against rapid degradation in primates. In this project, we propose in depth evaluation of these new drugs in poxvirus infected cells and in lethal animal models of orthopoxvirus disease. We will carry out studies to evaluate the effects of chemical structure on their metabolic stability in monkey liver S9 fractions, gastrointestinal transit and toxicity and test them in lethal animal models of poxvirus disease including, ectromelia, cowpox and vaccinia. Conventional poxvirus antivirals and the new metabolically stable analogs will be compared in an oral monkey pharmacokinetics proof of concept study. Several of these new compounds have a broad spectrum of antiviral activity against other viruses including the human immunodeficiency virus, herpes group viruses, hepatitis B and C viruses and polyoma virus and may find clinical uses for other diseases in addition to smallpox [unreadable] [unreadable] We have discovered several new antiviral drugs for the prevention and treatment of smallpox, an important threat agent for bioterrorism. In this project, we will select the most effective compounds and test them for metabolic stability in monkeys, the required model for FDA approval, and test their activity in lethal animal models of poxvirus disease. This project could lead to safer and more effective drugs for biodefense against smallpox as well as for civilian viral diseases because the agents are broad spectrum antivirals which are active against many viral infections. [unreadable] [unreadable] [unreadable]